This invention is directed to apparatus for grinding material to a desired fineness grade and to associated means for circulating material to effect a desired reduction of the material prior to evacuating the material after achieving desired fineness reduction.
It is known from U.S. Pat. No. 4,830,290 of May 16, 1989 to provide a roller mill with means in the grinding chamber for imparting an the upward lift to the material for improving the fluidization of material to maintain a substantially constant particle size for delivery to an outlet.
It is also known from U.S. Pat. No. 4,993,647 of Feb. 19, 1991 to operate material separator for obtaining refined material subject to a first reduction which moves the material into a separate where the large and/or heavier particles are returned by gravity to fall back into the first reduction for further reduction while the finer ground material is subjected to a second separation by a rotary device which alloys passage of particles of a smaller size while larger particles are refused passage and fall back for further reduction.
Some mills, as in U.S. Pat. No. 4,673,134 of Jun. 16, 1987, have a high throughput rate and effect a fine division as between fines and coarse particles in the outlet. In such mills the coarse particles can be removed by a pneumatic separator in that a rejecting grid is provided to include inclined blades which will retain very coarse particles.
It is also known from the system in U.S. Pat. No. 1,517,900 of Dec. 2, 1924 that small particles of solid material to be separated and graded or classified are fed into a separating chamber and air is caused to circulate through an endless path and through the separating chamber. In such a system the fine particles or "fines" are separated from the heavier or coarse particles or "tailings" within the separating chamber. Thus the "fines" are carried by the circulating air up through and out of the separating chamber while the "tailings" settle within the chamber and pass from the bottom thereof through a suitable discharge opening without further reduction.
To a lesser extent it is known from U.S. Pat. No. 2,099,505 of Nov. 16, 1937 to provide an efficient inexpensive apparatus which will clean seeds by means of air blasts and to provide means for equalizing the air blasts so the air is equally distributed throughout the apparatus. It is also known from the before listed U.S. Pat. No. 4,673,134 of Jun. 16, 1987 that mills in general are desired to have a high throughput rate and to effect a fine division with the amount of coarse particles in the outlet minimized, and in a more pertinent apparatus refined material is subject to a reduction in which the larger and heavier particles are separated out and returned by gravity to fall back into the first grind reduction for further reduction with the finer ground material being subject to a second separation by a rotary device.